The present description specifically discusses generation of a fluid pulse in a down hole drill string. However, it will be appreciated that the concept described herein may be applicable to any fluid line where it is desirable to create a fluid pulse and no limitation is intended thereby.
In the oil and gas exploration and extraction industries, a drill string is lowered into a bore. In such operations a drilling fluid known as “mud” is pumped from the surface through the drill string to exit from nozzles at the drill bit. The mud assists in dislodging and clearing material from the cutting face and carries the dislodged material through the drill bore to the surface.
It is well known in the industry that providing a pulsed fluid flow that can create a percussive or hammer effect can improve the drilling rate. The pulse of fluid flow is generated by periodically restricting the fluid flow so as to create a pressure difference. There are many different methods that have been proposed so as to restrict fluid flow.
One principle is to provide turbines, rotors or other means that can be driven by the fluid to operate a valve that can restrict flow. Such valves have an axially reciprocating poppet or piston that can cooperate with a narrowed bore so as to control fluid flow. The reciprocating movement is operated by a cam assembly that is driven by the rotating turbine.
Two examples of such a valve arrangement are provided in U.S. Pat. No. 4,830,122. In the first example, a cam follower or followers are fixed to the upstream end of a turbine for rotation. The follower(s) is operatively associated with a cam that is fixed against rotation. A piston or valve member is mounted to the piston. The action of the cam follower(s) upon the cam causes cyclical reciprocating movement of the cam and attached piston.
U.S. Pat. No. 4,830,122 also describes an alternate embodiment in which the cam and follower assembly are at the downstream end of the turbine. The cam is fixed against rotation such the cam action that occurs upon rotation of the turbine causes the entire turbine to reciprocate axially. The piston valve member is mounted to the upstream end of the turbine for cooperation with an annular valve ring.
U.S. Pat. No. 4,830,122 also teaches that the percussive effect caused by the pulsing action of the fluid can be further enhanced by connecting the pulse apparatus to a shock tool. A shock tool is a pressure responsive device that expands and contracts in response to varying fluid pressure. Shock tools are conventionally used to isolate the drill string from axial deflections produced by the bit during drilling operations. However, when a shock tool is operatively engaged with a fluid pulse apparatus the expansion and contraction of the shock tool can provide a percussive effect at the drill bit.
Since U.S. Pat. No. 4,830,122 has been published, there have been a number of different types of fluid pulse apparatus proposed for use with or without a shock tool. Such further fluid pulse tools have arrangements including rotating plates with axial flow openings that can open and close as a rotor is driven by the fluid.
U.S. Pat. No. 6,279,670 describes a down hole fluid flow pulsing apparatus having a valve member driven by a fluid actuated positive displacement motor to provide a varying fluid flow and a shock tool responsive to the varying fluid flow. Positive displacement motors have a power section comprised of a stator and a rotor. The stator consists of a steel tube that contains a bonded elastomer insert with a lobed, helical pattern bore through the centre. The rotor is a lobed helical steel rod. When the rotor is installed in the stator, the combination of the helical shapes and lobes form sealed cavities between the two components. When drilling fluid is forced though the power section the pressure drop across the cavities will cause the rotor to turn inside the stator. The valve that is operated by the positive displacement motor has a stationary valve plate and a valve plate that is rotated by the motor. The valves each have slots that move in and out of alignment during rotation of the rotatable plate, thereby creating a variable fluid flow.
While many of the fluid flow pulse devices described in the prior art have proven to be effective at increasing drilling penetration rates they have a number of disadvantages which has prevented their widespread adoption.
It is well known and appreciated in the drilling industry that it is difficult to design down hole tools which will operate reliably under the constantly changing properties of drilling mud and the constantly increasing hydrostatic pressure at down hole locations. This problem is exacerbated by the small space within which down hole tools must fit. In many drilling situations the down hole tools have an outside diameter of only 4¾ inches. These dimensional restraints impose onerous constraints on the design of such tools.
Further, many down hole tools have polymeric seals or elastomers. Such materials are subject to wear, abrasion by particles in the drilling fluid and can only be operated within certain temperature ranges and cannot be used with non-aqueous chemicals.
Despite the numerous prior art arrangements, there is constant desire in the oil and gas industry to provide fluid pulse apparatus that are cost effective to manufacture whilst being sufficiently robust to withstand the significant adverse operating conditions with minimal maintenance and associated down time. It will be appreciated that drill string downtime can have significant economic disadvantages.
It is therefore an object of the present disclosure to provide an alternative fluid pulse apparatus.